Apparatus for generating an accurately focused beam of charged particles and for related purposes



ugl, 1950 R. J. VAN DE GRAAFF ErAL 2,517,260

APPARATUS FOR GENERATING AN ACCURATELY FocUsED BEAM 0F CHARGED PARTICLES AND FOR RELATED PURPOSES Filed Sept. 18, 1945 5 Sheets-Sheet l Elven/iov@ ugl, R. J. VAN DE GRAAFF Erm.l

APPARATUS PoR GENERATING AN ACCURATELY FocUsED BEAM oF CHARGED PARTICLES AND PoR RELATED PURPOSES Filed sept. 18, 1945 3 Sheets-Sheet 2 2,5 l LY F'OCUSED BEAM 0F CHARGED PARTICLES AND FOR RELATED PURPOSES Filed Sept. 18, 1945 Aug l 1950 R. J. VAN DE GRAAFF ErAL APPARATUS FOR GENERATING AN ACCURATE 3 Sheets-Sheet 4I5 Invenom .ozer cI Van de ara/aff WIJK/Lila mWe'enBzcanez? t M MW.

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Patented ug. l, 11950 APPARATUS FOR GENERATING AN ACCU- RATELY FOCUSED BEAM F CHARGED PARTICLES AND FOR RELATED PURPOSES Robert J. Van de Graaff, Belmont, and iWilliam Weber Buechner, CambrdgeyMass., assignors, by mesne assignments, to Research Corporation, New York, N. Y., a corporation of New York Application September 18, 1945,*Serial No. 617,036 Claims. (ci. 'aso-146) This invention relates to apparatus for generating an accurately focused beam of charged particles, and for related purposes. In order that the broad principle of the invention may be readily understood, we have in the accompanying drawings disclosed a single embodiment or representation only, together with a slight modication, of apparatusindicative of the invention, by which apparatus the method herein disclosed may be practiced. Such method, however, is not herein claimed, but is claimed in our co-pending application Ser. No. 128,084, filed November 18, 1949.

The invention relates in part to the structure of an improved high voltage or like electronic vacuum tube for producing an accurately focused beam of swift particles, either electrons or ions. One means for providing a suitable source of high voltage for the operation of the high voltage tube is an electrostatic generator of the type described in prior patents to one of us, No. 1,991,236, dated February 12, 1935, and No. 2,230,473, dated February 4, 1941.

The apparatus herein disclosed and claimed and the disclosed but not herein claimed method,

make possible an improvement iny high voltage a: radiography and are applicable to high voltage ation. The apparatus and the herein disclosed but `not herein claimed method may be useful in such fields as nuclear physics, cancer therapy, radiography, highvoltage X-rays, the rectification of high voltage currents, the production of cathode rays and the acceleration of electrons l for high voltage electron microscopes.

The high voltage vacuum tube herein disclosed `to which, and to the method practiced in the herein disclosed use thereof, the disclosure particularly relates, is a constant potential X-ray tube of the order of two million volts, suitable i I for operation either sealed off or with a continuously operated vacuum pump.

The apparatus, comprising, as it does, a high voltage or like electronic tube of insulating material, has electrodes adapted to be connected to a suitable source of high potential, such as a high voltage electrostatic generator. At one end of the` tube, being the upper end as shown in the drawings, is locatedmeans providing an emitting source, which means in the present disclosure is a lament having a plane emitting surface of relatively minute area. The opposite end of the tube We refer to generically as the grounded end thereof. As will be subsequently described in detail, the wall of` the tube comprises electrode rings or ring-like disks or centrally-open metallic diaphragms arranged along the tube, spaced by insulation such as glass, and connected in suitable manner to the corresponding electrodes in a highvoltage generator in such a way that the potential gradient down the tube is uniform, and in such a way that equal steps in the voltage between successive electrodes are provided. Thus, there is provided in the tube a substantially uniform electrostatic field. The term metal or metallic includes any suitable conducting material.

An exceedingly important feature of the disclosure, both with respect to the apparatus herein claimed and with respect to the method not herein claimed, but claimed in said divisional application Ser. No. 128,084, is the provision and use ,of a substantially uniform electrostatic field which is in contrast with the use of a non-uniform electrostatic field, as has generally been the case in tubes that have been used in the past, as, for example, the tube disclosed in the patent to John G. Trump, No. 2,182,185, dated December 5, 1939.

The focusing of the electron beam by the herein disclosed vapparatus and bythe use of a substantially uniform electrostatic field, is less sensitive to variations in the potential applied to the various tube electrodes than is the case in tubes employing non-uniform electrostatic fields.

One advantage resulting from the use of a substantially uniform electrostatic eld, in combination with a magnetic lens in a high voltage vacuum tube, is that thereby extremely fine focusing is obtained of a high speed electron beam of the order of two million volts. Moreover, it appears that the construction referred to, one embodiment of which is herein disclosed, being simpler, is more reliable than prior constructions. The employment of a substantially uniform electrostatic field is materially associated with breaking up the voltage along the tube into very small divisions, which is also desirable from the point of view of insulating very high voltage.

With a uniform electrostatic field substantially the entire cross section of the high voltage or like electronic vacuum tube can be used for the acceleration of the charged particles, whereas in a non-uniform electrostatic field, as heretofore generally employed, the region which is usable for focusing is usually very close to the axis and is most eective only for the paraxial rays. Thus, with the use of a uniform electrostatic eld the electrons may be suitably accelerated through a region whose cross sectional diameter is relatively large when compared with the length of the high Voltage tube. A further advantage of the electrode configuration used, which breaks up the voltage as just stated, is that such conguration also minimizes the effect of any uncontrolled electric charges on the inner surface of the wall of the insulating material of the high voltage tube.

As far as we are aware a uniform electrostatic eld alone has never been used in high voltage vacuum tubes for accurate focusing prior to the present invention.

When substantially the entire acceleration of the electrons is done in a uniform electric eld, there is made a full and direct use of the longitudinal component of the electridiield, with a minimum interplay or even presence of the transverse component of the electric field, a `component in itself useless for the acceleration of the ions in the desired direction.

Heretofore in attempting to focus the electron beam, means have been used constituting a relatively complicated guidance or compulsion. It appears that, both in theory and in practice, if the electrons are permitted to fall in or be accelerated by a simple uniform electrostatic eld, the result is more satisfactory than the result obtained with more complicated means, the elements whereof require a certain definite, simultaneous adjustment relative to each other.

In some prior high voltage tubes a part only of the tube had a substantially uniform electrostatic eld, but in all such cases known to us the part of the field of such tubes that was non-unil. form in character was actually the part that was the most important of all as regards directing the v but mainly to simplify other features of the construction. An instance thereof is shown in the patent to Trump, No. 2,182,185, above referred to. ln certain other tubes of the prior art the very beginning of the path of the electrons or ions was l not in a uniform eld and was actually sharply distorted, so that there resulted an initial spontaneous breakdown creating a localized source of ionization by virtue of the fact that the electrostatic cld was extremely non-uniform in charac ter. Also in such instances in the prior art, tubes were made for operation with impulses where the voltage was on for periods of the order of only a few microseconds each, and in order to pass sufficient average currents they had to have high instantaneousl currents.

The momentary breakdown in the tube afforded extremely high instantaneous currents, so high that the accompanying space charge would tend to distort, during the moment of actual operation of the tube, the uniformity of the electric eld in regions which had been uniform just previous to the discharge.

In the apparatus herein disclosed as a representative embodiment of the invention herein claimed, in order to provide a path for the electrons or charged particles through the high voltage tube, preferably a two-inch diameter hole is cut out of or is otherwise provided at the center of and strike the target with an energy corresponding to the full generator voltage. The conditions are reversed when positive ions are to be accelerated. In their passage down the tube, they tend to follow the lines of electric force, and in the high voltage vacuum tube herein disclosed, the lines of force are straight lines. Consequently when the electrons or charged particles reach the bottom of the tube and strike the target, they are all traveling in parallel paths and all have the same energy. Such a result could hardly be secured where an alternating current device, such as a transformer, is used for the voltage source, because in such case the electrons usually have all energies ranging from some indeterminate low value up to that corresponding to the peak of the alternating current wave. There is thus an essentialdiiference between direct current equipment where all the electrons striking the target have the full generator energy, and all alternating current equipment where only a few of the electrons have the full rated peak voltage, the remainder being of lower energy. The structure herein disclosed is equally well suited for the acceleration of eitherpositive ions or negatively charged particles. This follows since the manner of construction and the use make the tube completely symmetric. Thus, it is possible to accelerate charges in either direction through the tube without the necessity of having to change the arrangement of potentials on the electrodes. The electrons are emitted at the negative end of the tube and are accelerated toward the electron-collecting target, while at the same time positive ions are to be produced at the positive end of the tube and accelerated toward the region of the cathode.

Other things being equal, the diameter of the beam of charged particles after passing through the tube is proportional to the size of the source of the charged particles. When the apparatus is used as an X-ray tube for radiography, the definition in the radiograph depends critically upon the spot size, and hence it is very desirable that the effective portion of the filament be as small as possible. vAs more fully set forth in the description of the drawings,` the focused spot upon the target can be smaller than 0.0'1 of an inch in diameter.

To obtain radiographs of thick sections having good definition, the size of the focal spot must be very small so that the X-rays will be emanating from a point source. Thick metallic sections of objects requiring on the order of two million volt X-rays present new geometric problems making essential the use of such size of focal spot. As stated, the high voltage or like electronic tube operates in conjunction with an electrostatic generator producing a potential ofthe order of two million volts. The use of such conetant potential has been found necessary in order to obtain and to maintain the extremely line focusing referred to and to provide optimum conditions for heat dissipation at the. focal point. As subsequently set forth in detail, the target upon which the electron beam is focused is a thick disk of gold used in association with high pressure water cooling. The use of such a relatively thick target disk permits operation with the target spot in molten condition without, however, melting entirely through the disk. It becomes possible as a result to make full use oi' the high intensity, sharply concentrated, electron beam and thus to obtainX-ray pictures of Vgreatly improved quality. lThe said targetconsisting of a animado thick disk of gold Lisnot :herein claimed, seither per se `or in combination, but, being itself an invention divisible from the rest of the apparatus, .though `desirably and for the best results used with `the other disclosed features of the apparatus, is claimed `per se and `in a substantially iuniform electrostatic field, in our co-pending apfpli-c-ationSer. No. 133,972, filed December 2), 1949, whioh co-pending application has been vdivifzled .out *from this application. The invention will be .better understood in detail Aby reference to the following description when 'taken in :connection with the accompanyring illustration of one specic embodiment of the apparatus and of one slight modification thereof, while the scope of the invention here- -in claimed will be ymore particularly pointed out in theappended claims.

In the drawings:

Fig. 1 is a vertical or longitudinal, central, cross `section of a high voltage vacuum tube illustra- `tive of the apparatus of the invention and by means of which the method herein disclosed but .not herein claimed vmay be practiced;

Fig; 2 is a transverse or cross section upon the line 2-2 of Fig. l;

Fig. 3 is a detail in vertical central section through the lower end of the iilament and `the surrounding guard ring;

Fig. 4 is a View similar to Fig. 3 but on a larger scale and representing only a portion of the guard ring;

Fig. 5 lis a broken-away detail in side elevation of a portion of the high voltage vacuum tube shown in Fig. l, with a diagrammatic indication of the connections between the electrede rings of the tube and corresponding electrodes of an electrostatic generator;

VFig. 6 `is a broken-away detail in vertical sec- .tion of a modied form of the electrode rings of `the high voltage tube at the lower portion of Said tube; and

Fig. 7 is a vertical cross sectional View of a high voltage rectifier that operates in accordance with many of the principles of the invention and representing one of the most important aspects thereof.

Referring to the drawings illustrating one embodiment only of the apparatus of the invention, together with a slight modification thereof, thereinis shown a high voltage vacuum tube consisting of a column composed of glass rings and of metal electrode rings or ring-like diaphragms or disks suitably welded together in alternation throughout the column, a part only of` which is shown, in a manner and by means not herein necessary to disclose in detail, inasmuch as such specific detail is not herein claimed, the present claimed disclosure being mainly, but not entirely, directed broadly to the herein disclosed but not herein claimed `method and the herein claimed apparatus by which a uniform electrostatic eld is provided and maintained in the tube or column, whereby in some applications, when the apparatus is used as an X-ray tube, the electron beam is controlled and compelled to strike the target at a point of exceedingly small diameter.

This configuration of electric field is also well suited for the acceleration and focusing of ion beams.

`In Fig. 1, the glass rings are respectively indicated at I, and the metal electrode rings, centrally open diaphragms or disks at 2. The said metal rings 2 or the like are electrode rings and lie accurately placed in planes perpendicular to the faxisiof the tube, and they .are placed 4at equal `distances apart, fas, for example, one-.third of van inch in the present disclosure. In Fig. 1,V the tube or column is represented as broken away because of the necessity of presenting a view of the complete tube 'in a single figure. While obviously the invention herein claimed is not limited to any particular size or proportion of parts, it is pointed out that in the illustrated embodiment of the high Voltage tube the distance in the actual structure from the horizontal line 3 to the horizontal line 4 is fifty-seven inches, the diameter of the opening in each ring 2 is two inches, and the outside diameter of the tube or column is three inches.V As clearly shown in Fig. 3, the outer edge of each of the metal electrode rings 2 is substantially coterminous with the outer edge Aof `the glass rings I. In the simplified form of lhigh voltage tube, represented in Fig. l, the distance from the line 3 to the top of the domelike glass insulation is about six inches. As stated, however, these dimensions may, within the principles of the invention herein claimed as apparatus, be varied as found suitable, and the scope of the invention herein claimed as apparatus is in no wise restricted by this recitation of dimensions. i

In the plane of the top metal electrode ring 2, a metal disk 5 is provided which substantially lls the opening inside said topmost metal ring 2, which disk 5 is maintained at the same potential as the top metal electrode 2. This insures that the electric iield immediately below the region of the disk '5 is uniform. The glass insulation which holds the metal disks 2 in correct relative alignment and which consists of the glass rings I, may have on its inner surface an uncontrolled distribution of electric charge which would tend to distort in a random and uncontrolled manner the uniformity of the electrostatic field within the main region of the tube. However, the disturbing influence of these charges is reduced to a negligible degree by the shielding eect of the metal rings 2, which extend inward from the glass wall composed of the glass rings `I toward the axis of the tube to a sufcient extent to produce the desired shielding. The fact that the gap between adjacent metal rings 2 is relatively small, being in the present embodiment of the apparatus one-third of an inch less the thickness of one disk, the actual structure having the other proportions above specified, makes it possible to obtain the desired shielding eiect with only a relatively narrow region or portion of each metal ring extending inwardly beyond the inner surface of the glass wall composed of the multiplicity of glass rings I.

In the disclosed embodiment of the apparatus the amount that each metal ring must project inward from the glass wall of the tube must be approximately the same as the length of the gap between next adjacent metal rings 2 all along the glass wall of the tube. Thus, the fact that in the disclosed embodiment of the apparatus the gap between the next adjacent metal rings 2 is small is in itself advantageous, inasmuch as it reduces the amount that each metal ring 2 must extend inward beyond the inner surface of the glass wall.

In order to obtain a uniform electrostatic eld, it is essential that the metal rings 2 be close to- |gether. rlhe fact that they are placed close together makes it possible to insulate a high voltage per unit length of the tube.

Moreover, the fact that the metal -rings 2 yare close together Imakes it possible to use more of the internal space in the tube for the beam-of charged particles.

Certain metal rings 2 of the tube or column,

Vwhich are indicated at 2a inFig. 5, are connected to corresponding electrodes of the generating apparatus which may take the form of a high voltage electrostatic generator, as indicated in the diagrammaticpart of Fig. 5 in such a Way that the voltage between the successive electrodes of the tube is the same.

In Fig. 5 a few of the generator electrodes are vrepresented at 2b, and a portion of the resistors at 2c. As shown, every third electrode ring 2 of the tube is connected to a corresponding electrode of the generator, which generator electrodes `,are an inch apart. Each of the metal electrode ordinary type of tube for the general purpose of the apparatus herein claimed, the electrical focusing was done by a series of what may be termed strong lenses which must have a very definite and specific relation to each other in order to produce the desired focusing action, and may be considered analogous to an optical system of a photographic camera involving a series of strong lenses of relatively short focal length.

In the disclosed high voltage vacuum tube and respecting the herein disclosed uniform electrostatic eld method of electrostatic focusing, it may be considered that the various electrical lenses have been reduced to Zero power, and in the optical analogy stated may be regarded as correspondingr to a series of flat plates of glass. f

Errors in the voltage between the electrodeswill thus have less effect` in disturbing the final focus in the case of an approximately uniform electrostatic eld than in the case of a strongly distorted electrostatic field.

To continue the analogy, where in a photographic camera a series of strong lenses is required which must have a definite relationship, any error in the strength of the lenses can upset such definite relationship. In a photographic camera the stronger the lens is the more accurate such a lens should be, and the more accurate should be its relation to all the other lenses of the camera.

As has been stated in the foregoing, the acceleration of an electron beam in a uniform eld has many basic advantages as contrasted with the more usual methods of acceleration in strongly non-uniform electric fields. However, it may be desirable while still using a substantially uniform electric eld for acceleration to modify it or warp it slightly, for example, in dealing with certain practical situations which would not arise in an entirely ideal case. In order to overcome the spreading effect, due to the space charge of a positive ion beam, it might be desirable to have the top part of the accelerating electric field slightly converging. This condition could be realized simply by having the voltage difference from electrode to electrode constant in the lower and middle portion of the tube, but this voltage difference slightly decreasing as the very top of the tube is approached.

Referring to .the use of the apparatus as an X-ray tube, lthe filament from which emanates the electron beam is indicated at l0 in Fig. i, and is shown in detail in Figs. 3 and 4. The said filament is composed of tungsten, and is of a hairpin type. It has the apex of the bend ground off, as indicated at Il in Figs. 3 and 4, in order to provide a plane emitting surface Il of relatively minute area. The diameter of the lament in the unreduced portion thereof is 0.010, and at the ground-off portion at the apex of the bend it is desirably less than one-half such thickness, thereby insuring an intense heat at said groundoff portion when the apparatus is in use, being the plane emitting surface of the electrons. The cross section of the filament being the least at the ground-olf portion, the resistance is the greatest at that area.

The filament l0 has placed in conjunction therewith and encircling the same, a guard ring I2, shown enlarged and in part in Fig. 4, Which vhas a plane lower surface lying exactly in the same plane as the emitting plane of the filament. The said guard ring l2 has therein a central through-opening I'Za, which is approximately 0.040 of an inch in diameter and within which the apex of the bend', constituting the plane emitting surface il, is symmetrically positioned.

The lament and the surrounding guard ring are usually maintained at approximately the same potential. However, by making the potential of the guard ring substantially more negative than that of the filament, the grid action of the guard ring can be used to reduce, or even entirely cut off, the electron stream. For this purpose there are shown in Fig. 4 wires ma and B2b leading respectively from the filament I0 and from the guard ring I2 to the positive and negative sides of a battery B, of about a hundred volts. Also the over-all focusing properties of the tube as a whole may be affected by providing relatively small Voltage differences between the filament and the surrounding guard ring. Thus, although the filament and the guard ring have been generally operated at the same potential, there are some occasions when it is desirable to operate the laiment and guard ring at somewhat differentpotentials.

By reason of the plane emitting surface H of the filament i0 and of the uniform field within the tube column, the beam of electrons proceeds in a substantially straight line along the tube or column from the point of emission, as indicated at l 3, resulting in a beam whose cross section in the region near the top of the tube corresponds closely to the size and shape of the emitting plane, and wherein the energy of the individual charged particles is substantially identical. Such a beam may readily be focused by arelatively weak magnetic field on an extremely concentrated spot, as by an electric magnet i4, the arrangement constituting a magnetic lens,the magnetic lines of force whereof are indicated at Illa.

Where the apparatus is used for generating X-rays, as for high voltage radiography, the electron beam is focused on a target which, while fully disclosed herein, is not herein claimed but is properly claimed per se in said divisional application Ser. No. 133,972. The said target is a thick metal disk l5 of gold, used in association with a high pressure water cooling jacket, indicated at i8, and provided with a water inlet I1 and water outlet IS. The target l5 is a gold disk one-quarter of an inch in thickness, as herein disclosed but not herein claimed, being, as stated,

properly claimed per se in our said (zo-pending 'application Ser. No. 133.972,.

r .2am-260 l i re With the usual construction `ior X-.ray targets, a high voltage beam of electrons ofgreat concentration would melt locally the target employed in such construction, and thus cause leakage of the cooling Water in the Avacuum `of the X-ray away. It is Yobserved in practice that the vapor ,3,

pressure of the liquid gold is so low,under the operating conditions in carrying out the herein disclosed, but not herein claimed method and in the ,use of the herein claimed apparatus, that the thinning of the target due to evaporation is negligible.

Although tungsten has generally been `used as a standard material for targets, experience with the gold targets herein disclosed but not herein claimed indicates `certain advantages. a high `heat conductivity and also chemical and `physical properties such that it can be repeatedly ,melted and .allowed to freeze Without appreciable oxidation or change in physical structure.

The high voltage vacuum tube herein illustrated and described constitutes one embodiment only of the apparatus herein claimed and presents the same in a simplified mechanical construction. Certain meohani'cal design features of the tube herein disclosed, such as are concerned with a vacuum-tight tube or column having the necessary insulating characteristics and enabling it to withstand the high pressures involved, as, `for example, an air p-ressure of from 200 to 400 pounds per square inch, have, in the further development of the tube herein described and claimed, been ably developed by Machlett Laboratories, Incorporated, to which has issued United States Patent No. 2,376,439, dated May 22, 1945, in the names of Raymond R. Machlett and Joseph W. Skehan, but not claiming subjects-matter herein claimed, and such .matters of mechanical construction are not herein claimed. The invention herein disclosed and the apparatus herein claimed are particularly directed to the use of a uniform electrostatic field 4for accelerating and focusing charged particles, and to an arrangement of electrodes particularly suitable for establishing and maintaining such an electric field, Aas well as the described use of a filament of a very small effective area. rIhe relatively thick target not herein claimed is claimed in our copending application Ser. No..133,972. The described and herein claimed construction `has the additional advantage of shielding the insulating walls of the tube, and breakingup the total -applied voltage so as to facilitate problems of insulation.

The present invention comprehends a high voltage vacuum tube adapted to the acceleration and focusing oi or like electronic charged particles, and in the case of electrons this beam is eX- tremely concentrated. t The apparatus herein claimed includes charged ,particle accelerating means providing a, uniform accelerating held, thus reducing to a minimumthe .dispersion of Ythe charged particles throughout their travel. Therefore a large number of accelerating sections are provided, the number used in present practice for two million voltsbeing `approximately 180, there:

Gold has y fili() 10 by'providing uniform accelerating steps of 12,000 volts each.

Thus, in such embodiment of the apparatus and referring again to Fig. 5, the electrode disks welded into the wall oi the tube in alternation with the insulating disks to constitute the `entire wall of the tube comprise sixty groups of metallic electrodes, each such group consisting oi three electrodes, and only one of said electrodes of which each such group is composed is directly electrically connected to a corresponding electrode or a high-voltage electrostatic generator, so that the voltage between the successive disks oi the tube is the same.

In Fig-6, there is represented upon an enlargedV scale a siight modication of the shape or form of certain of the electrode rings indicated at 2 in Figs. 1 and 5. In Fig. 6 there is shown in cross section a small portion only of the lower partei the tube. Therein the` .glass rings are indicated at i, as in Figs. l and 5. The electrode rings are indicated at iS, and each vof them has a .much thickened,l inwardly extending portion .26 of streamlined form and constituting what may `be termed a tear drop section. Such shape is evident from the cross sectional view. In reality each portion 20 is of annular form having extend-- ing ou't'ardly therefrom the thin rim-like part i9, thus constituting an annuiar iiange received between the next adjacent glass rings l. Electrede rings of tear drop shape are employed only at the lower end 4of that part `of the tube composed of alternating glass rings and metal rings.

Under certain conditions such tear drop construction oi electrodes may have advantages including the following: (l) improved electrostatic shielding of the inner wall of the insulating envelope of the tube; (2) increased shielding of the electron beam inside the tube against the disturbing effect of irregular `discharges on the :glass wall of the tube; (3) kby constructing the internal thick electrode Aof some suitable magnetic mate-- rial, such as soft iron, Athe electron beam can be shielded with greater eiiectiveness from disturbing external magnetic fields; (4) in certain special cases where -the .electric .field may locally depart from the uniiormcondition, as, for example, at .the lower end ofthe vacuum tube shown in Fig. 1, the rounding o the electrodes would prevent the concentrationof the electric held which .occurs with the useof ring-.plane electrodes 2 in this local region.

Another advantage of the use of a uniform electric iield for vthe acceleration of .charged parvticles may be noted here. AFor `a given voltage `and a given length oi-tube,the practice of such method (not herein claimed, but claimed in our co-pending application Ser. No. 128,084) limits Iloa `:minimum the values of the electric intensity or stress 4in the tube.` In `the herein disclosed, but not herein ,claimed method, for .pro-

-ducing an acceptably focused beam oi charged possible to apply to the tube its rated voltage even though the vacuum region of the tube may be temporarily filled with gas at the pressure surrounding the outer portion of the tube. lThis may be desirable for certain special tests, or when two or more tubes are connected in parallel with the same voltage source. In case of vacuum difficulty with one of the tubes, it could be allowed to ll with gas so that the other tube may continue to be used at full voltage. In our apparatus herein disclosed we emphasize that the multiplicity of metal electrode rings or conducting electrode members 2 are for the purpose primarily of establishing a substantially-uniform electrostatic field throughout the said tube, Iand in doing so we do not extend the outer edges of said members materially beyond, but, on the contrary, keep their outer edges substantially flush with, the outer edges of the insulating members l, and we avoid any construction which would cause, within the tube structure, any considerable amount of stored electric energy, as this would prevent the carrying out of our method not herein claimed, but claimed in our said co-pending application Ser. No. 128,084. We also avoid any construction that would provide appreciable capacitance between adjacent conducting electrode members 2, as this would prevent the carrying out of our method not herein claimed, but claimed in said co-pending application Ser. No. 128,084.

In Fig. 7 is suciently represented an improved high voltage rectifier possessing many of the principles set forth in the foregoing part of the specification, and which presents one of the most important aspects of the apparatus herein disclosed and claimed.

Therein is shown in vertical cross section a View of such a high voltage rectier, the interior of which is highly evacuated. In said figure, the emitter or cathode, being an approximately plane electron-emitting cathode, is indicated at 2l at the upper end thereof, and the anode is indicated at 22 at the lower end thereof. The cathode could be constructed by providing a large number of closely spaced, parallel wires heated by the passage of an electric current.

The outer, herein vertical, wall or main cylindrical portion of the rectifier is preferably composed, as in Fig. l, of alternate insulating rings 23, preferably of glass and of metal electrodes 24, which may be similar to those shown at 2 in Fig. 1 and possess the characteristics, purposes and advantages thereof.

Jackets for water coolingare provided at the upper and lower ends of the rectifier, as indicated at 25 and 25, and the outer surface of the main cylindrical portion of the rectifier will, if necessary, be cooled by circulating oil or gas.

The electron stream, so marked, is indicated at 2l, and the resistor at 28, which is indicative of a suitable generator such as would be employed with the apparatus shown in Fig. 1. A source of alternating voltage, such as a transformer, is diagrammatically indicated at 29 in proper relation to the high voltage rectifier.

The multi-sectioned construction, one embodiment of which is herein disclosed, makes possible the satisfactory insulation of extremely high inverse voltages, while some of the principles of electron now, as described in the preceding part of the specication, with relation to X-ray tubes, together with other aspects of the construction, make possible the flow of large electron currents 'in the desired direction. This is supported by the 12 fact that in tests with vX-ray tubes of the type described in the foregoing part of the speciiication, well-focused electron beams have been obtained at surprisingly low voltages.

In the multi-sectioned high voltage evacuated rectifier herein disclosed the electrons carrying the desired current move in paths substantially parallel. They travel in a ysubstantially uniform electric eld during the whole of their passage from cathode to anode. The electrons move'from cathode to anode through a region in which the electric component perpendicular to the main axis of the tube or rectifier is zero.

In such a multi-sectioned high voltage evacuated"'rectifier, thel maximum potential gradient on the electrodes in vacuum is a minimum, .and never exceeds a value approximately equal to the ratio of the maximum inverse voltage across the rectifier to the length of the electron path within the rectifier.

While there is herein shown and described one specific means for carrying into effect the principles which have been set forth, together with a slight modification of such specic means, it is understood that the invention herein claimed is not to be limited to the details of lconstruction shownand described or to the disclosed form or relative arrangement of parts, but that obvious modifications will occur to those skilled in the art.

The specific terms herein employed are used in a generic and descriptive sense and not for purposes of limitation.

What we claim' is:v

1. High voltage apparatus for generating an accurately focused beam of charged high-energy particles, comprising a high-voltage, high-vac- Inum, or like electronic tube having at one end an emission electrode and having an opposite grounded end, the wall of said tube between said emission electrode and said grounded end being wholly composed of a multiplicity of thin, metal, equal-diameter electrode disks all of substantially equal thickness, each having a central opening, the edges of all of which constitute a part of the inner face of the wall of the said tube, and a corresponding multiplicity of substantially equaldiameter insulating disks, all of substantially equal thickness but such that next adjacent electrode disks are close together throughout the tube to obtain a substantially uniform electrostatic field, each insulating disk having a central opening, said electrode disks and said insulating disks being ywelded together in face-contacting relation in alternation throughout the said tube, thereby to withstand very high external air or other gaseous pressureand having their outer edges substantially coterminous, the area of each of the metallic electrode disks at the outer edge of the insulating rings being of substantially the minimum extent possible consistent with the welding togetherl of said electrode disks and said insulating disks in face-to-face relation, so as to hold capacitance to a minimum and to hold to a minimum in the tube the intensity or stress of stored electric energy, the said tube of welded-together metallic electrode disks and insulating disks having means including said disks for establishing and maintaining therein, and for the passage of an accurately focused beam of charged particles, a substantially uniform electrostatic field parallel to the internal wall of said tube and throughout substantially the entire cross-sectional area thereof, from the said electrode having the emission area onward to an area suciently approaching the grounded end as to maintain such beam of charged particles in an essentially' direct', unvarying path through said substantially uniform electrostatic field, and as a beam of relativ-ely small cross-section between said electrodes.

2L High-voltage apparatus for generating an accurately focused beam of charged particles comprising, in combination, a greatly elongated, high-voltage, or like electronic vacuum tube made of a series of closely-spaced, similar, annular metallic electrode disks and annular sections of insulating material all of equal thickness, and which thickness is such that next adjacent metallic electrode disks are close together to obtain a uniform electrostatic eld, said sections of insulating material being sealed to opposite faces of the metal disks, thereby insulating said metal disks from one another and constituting the walls of said high-voltage vacuum tube, said tube having means for establishing andI maintaining therein, forthe passage of such accurately focused beam, a substantially uniform electrostatic field parallel to thesaid walls of such high-voltage vacuum tube and through substantially the entire cross-sectional area thereof, the area of each of the metallic electrode disks at the outer edge of the insulating rings being of the minimum extent possible consistent with the welding together of said elecrode disks and said insulating disks in faceto-face relation, so as to hold capacitance to a minimum and to hold to a minimum in the tube the tension or stress of stored electric energy, said high-voltage vacuum tube having at one end as a part* of said means a filament for emitting a beam of such particles, and a guard ring surrounding the emitting surface of said filament in I the plane of the emission surface of said filament, said high-voltage vacuum' tube having at the otherv end an anode constituting a target.

3". High-voltage apparatus on the order of Several million volts, for establishing and transmitting an accurately-focused beam of charged, swift particles, of relatively small cross-section in a substantially uniform electrostatic field extending throughout substantially the entire crosssectional area and throughout substantially the longitudinal extent of a high-voltage vacuum tube, comprising, in combination: a markedlyelongated high-voltage high-vacuum or like electronic small-diameter tube havingat its opposite ends respectively an emission electrode having a very small emission area constituting a source of charged, swift particles, and a grounded end; the wall of the said markedly elongated tube between said source of charged particles and said grounded end being wholly composed of a multiplicity of Very thin, fiat, substantially identical, substantially equal diameter, equal thickness, metal, electrode disks, each having a central opening, and a corresponding multiplicity of only slightly thicker, fiat, substantially equal diameter, substantially equal thickness, insulating disks, the said metal electrode disks the insulating disks alternating throughout said tube and having their faces in contact and welded together, and therefore providing a tube capable of withstanding very high external air or other gaseous pressure and having their outer edges substantially coter- Ininous and. non-protruding, throughout the length of the tube, the said electrode disks and the said insulating disks being of such degree of thinness that next adjacent electrode disks are close together and are uniformly spaced throughout the said tube, to cooperate in cbtaining a substantially uniform electrostatic field throughout substantially the 'longitudinal extent and substanf4, tiall'y throughout the entire cross-section of such tube, and which substantially uniform electrostatic field is throughout the length of the tube of markedly greater transverse area than thetransverse area off said beam of charged swift particles, each of such insulating disks having a central opening, the said multiplicity of metal electrode disks constituting a multiplicity of successivel groups, each group consisting of a plurality of such disks, and one disk only of each such group throughout the groups being directly electrically soconnected to a corresponding electrode' of a high- Voltage electrostatic generator that the voltage step between the successive disks of the tube is the same, the said emission electrode having its said very small emission area in the same transverse plane as the surface of the end electrode disk at that end of the said tube, and said electrode disksbeing non-connected electrically, whereby there is present a minimum of capacitance; andv means including said electrode disks so connected to the high-voltage electrostatic generator and also including said emission electrode having a very small emission area, for establishing in said tube a substantially uniform electrostatic field parallel to the internal wall of said tube and throughout substantially the entire cross-sectional area thereof from the said emission electrode having a very small emission area, onward to an area suiciently approaching they grounded end, so that the beam of charged particles is maintained in an essentially direct, unvarying path to said grounded end, and for establishing and transmitting a beam of charged, swift particles and for accurately focusing said beam of charged particles throughout its passage from said source of charged particles to said grounded end.

4. High-voltage apparatus in accordance with claim wherein each of said groups of electrode disks consist of three such disks.

5. An apparatus in accordance with claim 1, wherein the emission electrode has a guard ring surroundingl it, and which guard ring is of the same potential as the metal electrode disk next thereto, thereby insuring a uniform electrostatic field immediately below the region of the said guard ring.

6. An apparatus in accordance with claim l, wherein the said tube has the voltage difference from electrode disk to electrode disk constant in the lower and middle portions of the said tube, but having the voltage difference slightly decreasing as the very top of the said tube is approached.

7. Anapparatus in accordance with claim l, wherein the emission electrode has a guard ring surrounding it and the potential of which guard ring is substantially more negative than that of the emission electrode to reduce the stream of charged particles.

8. An apparatus in accordance with claim 1, wherein the said metal electrodes are so spaced and positioned in the wall of the tube and are so held in potential that the potential gradient at theA surface of the said disk electrodes within the tube nowhere substantially exceeds the value 0btained by dividing the voltage across the tube by the length ofthe said tube.

9. High voltage apparatus in accordance with claim l, wherein the metal electrode disk nearest the emission electrode has, in the horizontal plane of the inner face thereof, an inner metal disk substantially filling the central opening within said metal electrode disk, and itself having a central opening wherein isv received the said emissi-onelectrode, which emission electrode has `its emission area very small and in the horizontal plane of the inner face of the said inner metal disk.;

lil. vHigh voltage apparatus in accordance with claim l, wherein the metal electrode disk nearest theA emission electrode has, in the horizontal plane of the inner face thereof, an inner metal disk substantially iilling the central opening within said'metal electrode disk, and itself having a central opening wherein is received the said emission electrode, which emission electrode has its emission area very small and in the horizontal plane of the said inner metal disk, and wherein means is provided to maintain at the same potentialthe said inner metal disk and the said outer metal disk within the opening of which it is located.

1l. High voltage apparatus in accordance with claim i, wherein the metal electrode disk nearest the emission electrode has, in the horizontal plane of the-inner face thereof, an inner metal disk substantially filling the central opening Within said metal electrode disk, and itself having a central opening wherein is received the said emission electrode, which emission electrode has its emission area very small and in the horizontal plane of the inner face oi' the said inner metal disk, and wherein the said emission electrode is a filament of hairpin type, whereof the apex of the bend has been suiiiciently removed to provide said very Athin emission area.

12. High voltage apparatus in accordance with claim 3, wherein the said emission electrode having a very small emission area is of a hairpin type and is markedly further reduced in thickness at its apex to provide a very thin transmitting` area, and which area is surrounded by a guard ring, the -under face whereof is in the same transverse plane as the transmitting area of the said emission electrode.

13. High-voltage apparatus on the order of several million volts, for establishing and transmitting an accurately-focused beam of charged, swift particles, of relatively small cross-section in a substantially uniform electrostatic iield extending throughout substantially the entire crosssectional area and throughout substantially the longitudinal extent of a high-voltage or like electronic vacuum-tube, comprising, in combination: a markedly-elongated high-voltage high-vacuum or like electronic small-diameter tube having at its opposite ends respectively an emission electrode having a very small emission area constituting, a source of charged, swift particles, and a target electr-ode; the wall of the said markedly elongated tube between said source of charged particles and said target being wholly composed of a multiplicity of very thin, iiat, substantially identical, substantially equal diameter, substantially equal thickness, metal, electrode disks, each having a central opening, the edge of which constitutes a part of the inner surface of said tube,

' and a corresponding multiplicity of only slightly thicker, flat, substantially equal diameter, substantially equal thickness, insulating disks, the said metal electrode disks and the insulating disks having their faces in Contact and welded together, and therefore providing a tube capable of withstanding very high external air or other gaseous pressure and having their outer edges substantially coterminous and non-protruding, throughout the length of the tube, the saidfelectrode disks and the said insulating disks being of such degree of thinness that next adjacent electrode disks are close together and are uniformly spaced throughout the said tube, to cooperate in obtaining a substantially uniform electrostatic eld throughout substantially the longitudinal extent and substantially throughout the entire cross-section of such tube, each such insulating disk having a central opening, a multiplicity of said metallic electrode disks throughout the length or the said high-voltage tube being electrically connected to the corresponding electrodes of a high-voltage generator in a way thereby to provide a uniform potential gradient substantially all down the said tube from the cathode end thereof, and to provide equal steps in the voltage between successive electrode disks of the said tube, thereby estabiishing a substantially uniform electrostatic field, the said emission electrode having `its said very small emission area in the same transverse plane as the surface of the, end electrode disk at the cathode end of the said high-voltage tube, the said substantially uniform electrostatic iield extending suiliciently near the target electrode so that the beam of charged, swift particles is maintained in an essentially direct, unvarying path at high energies to said target electrode.

14. High-voltage apparatus for generating an accurately focused beam of charged particles, equally well suited for the acceleration of either positive ions or negatively charged particles, and whereby electrons may be emitted at the negative end of the apparatus and accelerated toward the electron-collecting target While at the same time positive ions are produced at the positive end of the said apparatus and are accelerated toward the region of the cathode, without changing the arrangement of potentials on the electrodes thereof, said apparatus comprising a, completely symmetric, greatly elongated, high-voltage, highvacuum, acceleration or like electronic tube having at its opposite ends a cathode emission electrode, and an anode target electrode, the wall of the said tube between said source of charged particles at the cathode end and said target at the anode end thereof being wholly composed of a multiplicity ci thin, metal, substantially equal diameter electrode disks all of substantially equal thickness, each having a central opening the edge of which constitutes a part of the inner surface of said tube, and non-connected electrically, and a corresponding multiplicity of substantially `equal-diameter insulating disks, each having a central opening and all of substantially equal thickness, but such that next adjacent electrode disks are close together throughout the tube to obtain a substantially uniform electrostatic field extending throughout substantially the entire cross-sectional area of the said tube and extending parallel to the internal wall 0f the said tube from lthe source of charged particles at the cathode end of the tube onward to an area suliciently nearing the anode target electrode as to maintain such beam of charged particles in an essentially direct, unvarying path through said substantially uniform electrostatic eld, and as a beam of relatively small cross section between the cathode electrode and the anode electrode, said electrode disks and said insulating disks constituting the wall ofthe said tube being welded together in face-contacting relation in alternation throughout the said greatly elongated tube, thereby to withstand very high external air or other gaseous pressure, the outer edges of said electrode disks and of said insulating disks all being substantially coterminous and substantially non-protruding and together forming the outer wall of `the saidtube, a multiplicity of the said metallic electrodes along the tube being connected to corresponding electrodes of a high voltage electrostatic generator, to establish the same voltage steps between the successive disk electrodes `throughout the tube, and providing equal steps in the voltage between successive electrode disks of the said tube.

15. A system or apparatus for generating,

maintaining and transmitting an accurately focused beam of charged particles, comprising a Vhigh voltage or like electronic vacuum tube, the

lateral wall whereof is composed throughout its length of a multiplicity of thin, flat, substantially identical, substantially equal diameter, substantially equal thickness, metal electrode disks, each having a central opening within said tube, and a like multiplicity of only slightly thicker, flat, substantally equal diameter, insulating disks, each having a central opening constituting a part of the wall of said tube, the said metal electrode disks and the said insulating disks directly alternating `throughout said tube, and having their faces in contact and welded together, and therefore providing a tube capable of withstanding very high Aexternal air or other gaseous pressure, the outer `edges of the said electrode disks and insulating disks being substantially co-terminous throughout the length of said tube, the said electrode disks being non-connected to each other electrically, whereby there is present a minimum of capacitance, the said electrode disks preesnting a multiplicity of successive groups and one electrode disk only of each group being directly connected electrically to a corresponding electrode of a high voltage electrostatic generator, so` that the voltage step between the successive electrode disks of the tube is the same, an emission electrode at one .lend of said tube having a very small emission area, said tube having an opposite grounded end,

and means including said electrode disks so connected electrically to corresponding electrodes of a high voltage generator and including said emission electrode to establish in said tube a substantially uniform electrostatic field parallel to the internal wall of said tube and extending through- .tout substantially the entire cross sectional area thereof from the said emissionelectrode having a very small emission area onward to an area sufficiently approaching the grounded end, which ,wall composed of alternate metallic electrode disks and insulation rings united in face-to-face contact, one end of said tube having a continuous filament of hairpin shape for emitting a beam of such particles, said filament having the outer part only `of the apex of the bend of such filament markedly reduced in diameter to provide a very small, flat, emission surface, said filament being otherwise of non-reduced diameter, said tube having a guard ring surrounding the emitting .surface of said filament and having the inner face of said guard ring located in the transverse i8 plane of the said small, flat, emission surface of said filament,` the lament receiving opening of the said guard ring being but very slightly greater in diameter than the apex of said filament, the

said lower surface of said guard ring lying in the same transverse plane as the lower surface of the final electrode disk at that end of the tube, and which final electrode disk surrounds said guard r1ng.

17. High-voltage apparatus for generating a accurately focused beam of charged particles comprising, in combination, an elongated, highvoltage, or like electronic vacuum-tube of insulating material provided with opposite electrodes, and means for establishing and maintaining throughout said tube, for the passage of such accurately focused beam, a, substantially uniform electrostatic field extending parallel to the walls of the tube from the electrode having the emission area onward to an area sufliciently approach- `ing `the other electrode, so as to maintain such beam of charged particles in an essentially direct, unvarying path throughout said substantially uniform electrostatic field, the wall of the said high voltage tube from the emission area of the charged particles onward to an area sufficiently approaching the other electrode being composed of alternating rings of insulating m'aterial and of metal constituting electrodes, at least one of the said electrode rings being a substantially thickened, inwardly extending portion to provide improved electrostatic shielding at the inner wall of said tube.

18. High-voltage apparatus for generating an accurately focused beam of charged particles comprising, in combination, an elongated, highvoltage, vacuum-tube of insulating material provided vvith opposite electrodes, and means for establishing and maintaining throughout said tube, for the passage of such accurately focused beam, a substantially uniform electrostatic field extending parallel to the walls of the tube from the electrode having the emission area onward to an area suciently approaching the other electrode, so as to maintain such beam of charged particles in an essentially direct, unvarying path throughout said substantially uniform electrostatic leld, the wall of the said high voltage tube from the emission area of the charged particles onwardv to an area suiiiciently approaching the other electrode, being composed of alternating rings of glass and of metal constituting electrodes, at least one of the lowermost electrode rings being a substantially thickened, inwardly extending portion to provide improved electrostatic shielding at the inner Wall of said tube.

- 19. High-voltage apparatus for generating an accurately focused beam of charged particles comprising, in combination, an elongated, highvoltage, vacuum-tube of insulating material provided `with opposite electrodes, and means for establishing and maintaining throughout said tube, for the passage of such accurately focused beam, a substantially uniform electrostatic field extending parallel to the walls of the tube from the electrode having the emission area onward to an area suciently approaching the other electrode, so as to maintain such beam of charged particles in an essentially direct, unvarying path throughout said substantially uniform electrostatic field, the wall of the said high voltage tube from the emission area of the charged particles ,onward to an area suiiiciently approaching the other electrode, being composed of alternating rings of glass and of metal constituting electrodes,

aseriesconstituting theilowermost electrode rings loeingk substantiallyV thickened inwardly f the glass. rings to provide improved electrostatic shielding;

- ,20; High-voltage apparatus for generating an accurately focused beam of: charged particles comprising, in combination, anv elongated, high'- voltage, vacuum-tube of insulating material provided with opposite electrodes, and means( for establishing and maintaining throughout said tube'pfor the passage of such accurately focused beam, asubstantially uniform electrostaticI field extending parallel to the walls-of the tube from thezelectrode having the emission area onward to .anareasuiiiciently approaching' the other electrodeyso* as to maintain; suchrbeam -of charged particles in an essentially direct, unvarying path Y throughout saidv substantially uniform.v electrostatic eld, the wall ofthe said high voltage tube lfrom lthe emission area of the charged particles ameter electrode disks, all of equal thickness,

each having a central opening, anda correspondingmultiplicity of equal-diameter insulating disks all ofequal thickness. but suchthat each next adjacent electrode disks are close together tor obtain ay substantially uniform electrostatic eld,

each insulating diskrhaving a central opening, said electrode disks and saidinsulating disks being.` Welded together in face-contacting relation in` alternation throughout to` provide a greatly elongated rectifier capable. of withstanding, very high external air orY other gaseous pressure, the

out'er.v edges of saidv electrode disksbeingcoterminous .with the: outer` edges` of the said: insulating .disksysaidrectier having means to compel the electrons carrying the desired current tovmove in kpaths,-substantially parallel, and includingmeans electrically connecting` theA outer edges of said electrode disks individually witha source of alternating voltage.

v 22: A multisectioned"high voltage: evacuated rectifierhaving at opposite ends thereof an emission electrode and a target: electrode, the-:wallof `thev said rectifier betweenfsaid emission electrode ,andf said target electrode beingwhollycomposed ofal multiplicityI of thinmetal, equal-diameter electrode disksall of equal thickness, each having acentral opening, and a corresponding multiplicity of f equal-diameter insulating disks all ofiequal thickness but suchkthat each next adjacent electrode disks areclose together to obtain a substantially uniform electrostatic field, each insulating disk having a central opening, said electrodedisks and'said insulatingdisks being welded together in face-contacting relation inl alternation throughout to provide a greatly elongatedrectiiier capable lof withstanding Very high externalair or other gaseous pressure', the outer edgesof said electrode disks being coterminous with the outer edges of the said insulating disks, said-rectifier having means to compel the lelecv`irons` carryingthe desired currentto travel ini a substantiallyuniform'f electric fleldxduring the wholef of-ntheirf passage from cathode toY anode, and-:to establish and maintain such an electric eld' in said: rectifier, said means' including electricalconne'ctions between the` outer edges of the said electrode disksv and a` source of alternating voltage.

23. A multi-sectioned high voltage.1r .evacuated rectierhaving at opposite ends thereof an emission,v electrode and. a targetelectrode, the wall` of the` said rectierbetween said emission electrode andsaid target electrode being Wholly composed of arm'ultiplicity, of. thin, metal, equal-diameter electrode. disks, kall of'.l equal thickness,. each: havfingiacentral opening, and ai corresponding multiplicity of equal-diameter insulating disksall of equal thicknessfbut such that eachnext adjacent electrodedisksareclose together to obtain a sub'- stantially uniform electrostatic field, each' in'- sulatingzdisk .havingga central opening, saidelectrode. disks andsaid insulating disksrbeingiweld edftogetlier in face-contacting: relation in alternationthroughout to provide aI greatly, elongated rectifier capable" of'withstandin'g very highfex- ,ternar air or other'` gaseous pressure,.the outer edges'ot said' electrode disks being coterminous with the outer edges of the said insulating disks, saidrectiiier. having" means to compel the electrons to move froml cathode to anode through' a ,regionin'y whichithe electric component perpendicular to the main axis of the tube or rectifier is zerogand .to establish and maintain such an elec'- tri'c field? in said rectifier, said meansr including electrical connections between the'outer edges of the' said' electrode'f disks and' a source of alternating. voltage.

24a A multi-sectioned' high voltage evacuated reotiiierhaving atfoppositefendsf thereof an emission. electrodev anda target electrode, the wall ofther saidv rectifier between said emission electrodeandfsaid 'targetl electrode being wholly cornposed'o't allmultiplicity'off thin, metal, equal'- diameter'electrodedisks, all: ofr equal thickness, each having a1 central opening,- and a" corresponding multiplicity of: equal-diameter insulating disks all ofy equall thickness but suchzthat each next adjacent electrode disks are-close'together to obtain ,al substantially uniformA electrostatic field each insulatingJ disk having a central opening, said electrode disks-v and said" insulating disks` being welded togetherin'face-contacting relation in alternation throughout to provide a greatly elongatedrectifier capablel ofA withstanding very high 'externallair or other. gaseous pressure,y the outer edges.' off saidi electrode disks being' coterminous with` the outer,- edges of f the-said` insulatingfdisks, saidrectiler havingmeans tov establish an electronic; path f therein, and; including means electrically connectingithe. outeredges ofsaid electrede,diskszindividually witha source of alternating Voltage, and'in which rectier'the maximum potentialggra'dient is arminirnum'. on the electrodes thereof; that are:in vacuum,

25er-l: multisectioned high voltage evacuated rectier' having at opposite ends thereof an emissioni electrode and a target electrode, the wall of the :said 'rectierf between saidemission electrode and-said target electrode` being wholly composed ofxamultiplicity' ofl thin, metal, equal-diameter electrode disks, all of equalthickness', each lha-viri'g ai central opening, and a corresponding multi'- plicity of equal-diameter!insulating disksall of equal thickness'. but'isu'c'h that each. nextl adjacent :electrode disks .are close; together tol` obtain a' sub'- v.ssantiallyl uniform.'Y electrostaticifield, eachM iii- 21 sulating disk having a central opening, said electrode disks and said insulating disks being welded together in face-contacting relation in alternation throughout to provide a greatly elongated rectifier capable of withstanding very high external air or other gaseous pressure, the outer edges of said electrode disks being coterminous with the outer edges of the said insulating disks, said rectifier having means to establish an electronic path therein, and including means electrically connecting the outer edges of said electrode disks individually with a source of alternating voltage, and in which rectifier the maximum potential gradient occurring on the portion of the electrodes that are in vacuum never exceeds a value approximately equal to the ratio of the maximum inverse voltage across the rectifier to the length of the electron path within the rectier.

ROBERT J. VAN nn GRAAFF. WILLIAM WEBER BUECHNER.

. 22 REFERENCES CITED 'UNITED STATES PATETS Number' Name Date Re; 18,694 Mutscheller Dec. 20, 1932 2,043,733 Brasch et al June 9, 1936 V2,110,911 Knoll et a1. Mar. 15, 1938 2,145,727 Lloyd, Jr Jan. 31, 1939 2,168,780 Olshevsky Aug. 8, 1939 2,182,185 Trump Dec. 5, 1939 2,272,374 Kallmann et al. Feb. 10, 1942 2,376,439 I Machlett et al May 22, 1945 

